1. Field of the Invention
The present invention relates to a sheet feeding apparatus for feeding a sheet.
In the present invention, the term “sheet” includes a recording sheets made of paper or other material, and the term “substantially vertical” includes “vertical”.
2. Description of the Related Art
FIG. 10 is a cross sectional view showing a first sheet feeding apparatus 1 according to related art. The first sheet feeding apparatus 1 of the related art includes a tray 3, a feed roller 4, a lifting plate 5, a separator plate 6, a spring 7, and a biasing spring 8. Sheets 2 are stacked on the lifting plate 5 in the tray 3. The feed roller 4 is disposed on the side of the stacked sheets 2 opposite from the side thereof supported on the lifting plate 5. The lifting plate 5 is mounted so as to be movable toward and away from the feed roller 4. The lifting plate 5 is biased toward the feed roller 4 by means of the spring 7, and holds the sheets 2 by cooperating with the feed roller 4. The separator plate 6 is disposed opposite the feed roller 4 on the downstream side of the tray 3 as viewed in a sheet feeding direction A1, and is biased by the biasing spring 8 into contact with the feed roller 4.
When the feed roller 4 is rotated, sheets 2 are fed to the position between the feed roller 4 and the separator plate 6 arranged downstream in the sheet feeding direction A1, and the sheets 2 are thus held between the feed roller 4 and the separator plate 6. Of the sheets 2 held between the feed roller 4 and the separator plate 6, only one sheet 2a closest to the feed roller 4 is separated by the separator plate 6, and transported to the position between a pinch roller 9 disposed downstream in the sheet feeding direction A1 and a transport roller 10 disclosed opposite the pinch roller 9. Of the sheets 2 held between the feed roller 4 and the separator plate 6, the remaining sheets, i.e., the sheets excluding the one sheet 2a, are not transported in the sheet feeding direction A1 but remain held between the feed roller 4 and the separator plate 6.
The one sheet 2a that has been transported by the feed roller 4 to the position between the pinch roller 9 and the transport roller 10 is further transported downstream in the sheet feeding direction A1 while being held between the pinch roller 9 and the transport roller 10 as well as between the feed roller 4 and the separator plate 6. After that, the upstream end of the one sheet 2a, as viewed in the sheet feeding direction A1, is gripped between the feed roller 4 and the separator plate 6. As the one sheet 2a is fed incrementally by a predetermined feed amount downstream in the sheet feeding direction A1 by means of the pinch roller 9 and the transport roller 10, an image is formed on the one sheet 2a by a print head 12 of a printer mechanism 11.
FIG. 11 is a cross sectional view showing second sheet feeding apparatus 15 according to the related art. In the second feeding apparatus 15, the construction except that of the feed roller 16 is the same as the construction of the first sheet feeding apparatus 1 of the related art, and corresponding parts are therefore designated by the same reference numerals. The feed roller 16 has a cut portion 16b formed by cutting one side flat, and a roller contacting portion 16a formed from the cylindrically faced remaining portion, i.e., the portion excluding the side cut portion 16b. The feed roller 16 is disposed on the side of the stacked sheets 2 opposite from the side thereof supported on the lifting plate 5.
When the feed roller 16 is rotated while holding the sheets 2 between the lifting plate 5 and the roller contacting portion 16a of the feed roller 16, some of the upper sheets 2 are fed to the position between the feed roller 16 and the separator plate 6 arranged downstream in the sheet feeding direction A1. Of the sheets 2 held between the feed roller 16 and the separator plate 6, only the one sheet 2a is separated by the separator plate 6, and transported to the position between the pinch roller 9 and the transport roller 10 arranged downstream in the sheet feeding direction A1. When the one sheet 2a is transported to the position between the pinch roller 9 and the transport roller 10, the cut portion 16b, instead of the roller contacting portion 16a, comes to face the one sheet 2a. As a result, the one sheet 2a is separated from the feed roller 16, and transported by means of the pinch roller 9 and the transport roller 10 by being held between the pinch roller 9 and the transport roller 10.
FIG. 12 is a cross sectional view showing a third sheet feeding apparatus 20 according to the related art. The third sheet feeding apparatus 20 of the related art includes a tray 22, a lifting plate 23, a feed roller 24, a spring 25, and an auxiliary roller 26. Sheets 21 are stacked on the lifting plate 23 in the tray 22. A limiting plate 22a, which is disposed integrally with the tray 22, is located downstream of the sheets 21 in the feeding direction A2, and comprises a portion whose cross section taken perpendicularly to a sheet feeding direction A2 is substantially L shaped, more specifically, a portion extending toward the feed roller 24 and a portion formed so as to extend from the downstream to the upstream side in the sheet feeding direction A2. The leading edges of the sheets 21 stacked on the lifting plate 23 abut the limiting plate 22a. The feed roller 24 is disposed on the side of the stacked sheets 21 opposite from the side thereof supported on the lifting plate 23. The lifting plate 23 is mounted so as to be movable toward and away from the feed roller 24. The lifting plate 23 is biased toward the feed roller 24 by means of the spring 25, and holds the sheets 21 by cooperating with the feed roller 24. The auxiliary roller 26 is disposed on the same side as the feed roller 24 with respect to the sheets 21 stacked on the lifting plate 23. The auxiliary roller 26 is mounted rotatably about the axis of rotation of the feed roller 24. Further, the auxiliary roller 26 is located nearer to the sheets 21 than the feed roller 24 is, and rotates about its axis of rotation extending parallel to the axis of rotation of the feed roller 24.
When the feed roller 24 is rotated while holding the sheets 21 between the feed roller 24 and the lifting plate 23, one sheet 21a closest to the feed roller 24 is fed out with its leading edge riding over the limiting plate 22a, and is thus advanced to a pair of transport rollers 27 disposed downstream in the sheet feeding direction A2. When the one sheet 21a is fed to the position between the pair of transport rollers 27, the feed roller 24 and the pair of transport rollers 27 rotate in such a manner as to feed the one sheet 21a in the direction opposite to the sheet feeding direction A2. With the feed roller 24 rotating in this manner, the auxiliary roller 26 presses the one sheet 21a and the remaining sheets 21 excluding the one sheet 21a, and the one sheet 21a is thus separated from the feed roller 24. With the one sheet 21a held between the lifting plate 23 and the auxiliary roller 26 as well as between the pair of transport rollers 27, the feed roller 24 and the pair of transport rollers 27 are rotated to transport the one sheet 21a downstream in the sheet feeding direction A2.
FIG. 13 is a cross sectional view showing a fourth sheet feeding apparatus 30 according to the related art. The sheet feeding apparatus 30 of the related art includes a lifting plate 32, a feed roller 33, a limiting plate 34, and a pair of transport rollers 35. Sheets 31 are stacked on the lifting plate 32. The lifting plate 32 is mounted so as to be movable toward and away from the feed roller 33, while the feed roller 33 is disposed on the side of the stacked sheets 31 opposite from the side thereof supported on the lifting plate 32. The lifting plate 32 is provided with a protruding portion 32a protruding toward the feed roller 33. The drive shaft 33a of the feed roller 33 is provided with an engaging portion 33b which rotates with the rotation of the feed roller 33 and engages with the protruding portion 32a of the lifting plate 32. The lifting plate 32 is biased toward the feed roller 33, and holds the sheets 31 by cooperating with the feed roller 33. The limiting plate 34 is a plate-like member which is formed perpendicularly to a sheet feeding direction A3 and fixed in position on the downstream side of the lifting plate 32 as viewed in the sheet feeding direction A3 . The leading edges of the sheets 31 stacked on the lifting plate 32 abut the limiting plate 34. The pair of transport rollers 35 are disposed on the downstream side of the limiting plate 34 as viewed in the sheet feeding direction A3.
When the feed roller 33 is rotated while holding the sheets 31 between the lifting plate 32 and the feed roller 33, one sheet 31a closest to the feed roller 33 is fed out with its leading edge riding over the limiting plate 34, and is thus advanced to the pair of transport rollers 35 disposed downstream in the sheet feeding direction A3. With the rotation of the feed roller 33, the engaging portion 33b rotates until it engages with the protruding portion 32a of the lifting plate 32. This releases the holding of the one sheet 31a by the feed roller 33 and the lifting plate 32, and the one sheet 31a is transported downstream in the sheet feeding direction A3 by the pair of transport rollers 35 alone.
FIG. 14 is a cross sectional view showing a fifth sheet feeding apparatus 40 according to the related art. The fifth sheet feeding apparatus 40 of the related art includes a limiting plate 44, a lifting plate 42, a feed roller 43, a spring 45, a separator plate 46, a biasing spring 47, and an actuator arm 48. The lifting plate 42 is mounted so as to be movable toward and away from the feed roller 43, and sheets 41 are stacked on the lifting plate 42. The feed roller 43 is disposed on the side of the stacked sheets 41 opposite from the side thereof supported on the lifting plate 42. The lifting plate 42 is held engaged in such a position as to keep the sheets 41 separated from the feed roller 43 as shown by solid lines in FIG. 14 until the feed operation of the sheets 41 is started; when starting the feed operation of the sheets 41, the lifting plate 42 is disengaged, and holds the sheets 41 by the biasing force of the spring 45 by cooperating with the feed roller 43 as shown by imaginary lines in FIG. 14. The limiting plate 44 is a plate-like member which is disposed with its one end spaced apart from the feed roller. The limiting plate 44 is formed perpendicularly to a sheet feeding direction A4, and is disposed on the downstream side of the lifting plate 42 as viewed in the sheet feeding direction A4. The separator plate 46 is disposed opposite the feed roller 43 on the downstream side of the limiting plate 44 as viewed in the sheet feeding direction A4. The downstream end of the separator plate 46, as viewed in the sheet feeding direction A4, is supported so as to be angularly movable about an axis extending perpendicularly to the sheet feeding direction A4; the separator plate 46 is brought into contact with the feed roller 43 by being biased toward the feed roller 43 by means of the biasing spring 47. The actuator arm 48 is disposed on the upstream side of the separator plate 46 as viewed in the sheet feeding direction A4, and mounted so as to be angularly movable about an axis extending parallel to the width direction of the transport path along which the sheet is transported. The actuator arm 48 presses the separator plate 46 to separate it from the feed roller 43.
When the lifting plate 42 is disengaged as described above, the stacked sheets 41 are displaced in a direction toward the feed roller 43 by the biasing force of the spring 45. Before the sheets 41 are sandwiched between the lifting plate 42 and the feed roller 43, a plurality of sheets 41 including one sheet 41a closest to the feed roller 43 are allowed to run over the limiting plate 44 in the downstream direction along the sheet feeding direction A4. When the feed roller 43 is rotated after the sheets have been held between the lifting plate 42 and the feed roller 43, the one sheet 41a is separated by the separator plate 46 from the remaining sheets 41 excluding the one sheet 41a, and the one sheet 41a is transported downstream in the sheet feeding direction A4. When the one sheet 41a is separated by the separator means 46, the lifting plate 42 is moved in a direction away from the feed roller 43, thus releasing the holding of the sheets 41 by the feed roller 43 and the lifting plate 42. Thereafter, when the one sheet 41a is detected reaching the position between a pair of transport rollers disposed downstream in the sheet feeding direction A4, the separator plate 46 is separated from the feed roller 43 by the action of the actuator arm 48 and, in this condition, the one sheet 41a is transported downstream in the sheet feeding direction A4.
FIG. 15 is a cross sectional view showing a sixth sheet feeding apparatus 50 according to the related art. The sixth sheet feeding apparatus 50 of the related art includes a lifting plate 52, a feed roller 53, an idle roller 54, a separator plate 55, and a push-back means 56. Sheets 51 are stacked on the lifting plate 52. The lifting plate 52 is mounted so as to be movable toward and away from the feed roller 53. The feed roller 53 is disposed on the side of the stacked sheets 51 opposite from the side thereof supported on the lifting plate 52, and holds the sheet 51a by cooperating with the lifting plate 52. The idle roller 54 is mounted so as to be movable about an axis extending parallel to the width direction of the transport path along which the sheet is transported, and is disposed spaced apart in the width direction from the feed roller 53. The idle roller 54 is disposed in contacting relationship with the separator plate 55. The separator plate 55 is disposed opposite the feed roller 53 and the idle roller 54 on the downstream side of the lifting plate 52 as viewed in a sheet feeding direction A5. When the lifting plate 52 is moved toward the feed roller 53, the pushing of the separator plate 55 by the lifting plate 52 is released and moves toward the feed roller 53; when the lifting plate 52 is moved in a direction away from the feed roller 53, the separator plate 55 is separated from the feed roller 53 by being pressed by the lifting plate 52. The push-back means 56 is disposed downstream of the lifting plate 52 in the sheet feeding direction A5, and works to hold back the remaining sheets 51, excluding the one sheet 51a closest to the feed roller 53, toward the upstream side of the sheet feeding direction A5 after the one sheet 51a has been separated from the remaining sheets 51 by the separator plate 55.
When the feed roller 53 is rotated while holding the sheets 51 between the lifting plate 52 and the feed roller 53, the sheets 51 are fed to the position between the feed roller 53 and the separator plate 55 and between the idle roller 54 and the separator plate 55. The one sheet 51a is separated from the remaining sheet 51 by the separator plate 55 and transported to the position between a pair of transport rollers disposed downstream in the sheet feeding direction A5. When the one sheet 51a is fed to the position between the pair of transport rollers, the lifting plate 52 is moved in a direction away from the feed roller 53 and presses the separator plate 55. This causes the separator plate 55 with the idle roller 54 contacting thereon to move away from the feed roller 53, thereby releasing the holding of the sheets 51 by the separator plate 55 and the feed roller 53. The one sheet 51a, while being held between the pair of transport rollers as well as between the idle roller 54 and the separator plate 55, is transported downstream in the sheet feeding direction A5. The remaining sheets 51 are not transported downstream in the sheet feeding direction A5, but remain held between the idle roller 54 and the separator plate 55. When the one sheet 51a is transported downstream in the sheet feeding direction A5 by the pair of transport rollers, and is fed out of the machine after an image is formed on the one sheet 51a, the remaining sheets 51 are pushed back by the push-back means 56 toward the upstream side of the sheet feeding direction A5.
In the first sheet feeding apparatus 1 of the related art, when the one sheet 2a is transported by the pinch roller 9 and the transport roller 10, the one sheet 2a is held between the feed roller 4 and the separator plate 6 as well as between the pinch roller 9 and the transport roller 10. When the one sheet 2a is kept held between the feed roller 4 and the separator plate 6 as well as between the pinch roller 9 and the transport roller 10, back tension acting in the direction opposite to the sheet feeding direction A1 is exerted on the one sheet 2a since the upstream end thereof as viewed in the sheet feeding direction A1 is held between the feed roller 4 and the separator plate 6. This back tension is an unstable force that changes as the one sheet 2a is transported downstream in the sheet feeding direction A1. In particular, when the holding of one sheet 2a by the feed roller 4 and the separator plate 6 is released, the back tension being exerted on the one sheet 2a changes abruptly. This can cause a variation in the feed amount by which the one sheet 2a is fed downstream in the sheet feeding direction A1, resulting in skewed feeding with respect to the sheet feeding direction A1. Therefore, a high quality image cannot be formed on the sheet 2.
In the second sheet feeding apparatus 15 of the related art, the occurrence of back tension can be prevented by forming the cut portion 16b on the feed roller 16, but the remaining sheets are separated from the feed roller 16 and the holding of the remaining sheets by the feed roller 16 and the separator plate 6 is released. As a result, the remaining sheets slide downward in the downstream direction along the sheet feeding direction A1, and this can cause a double feed, a phenomenon in which more than one sheet 2 is fed out simultaneously downstream in the sheet feeding direction A1, when performing sheet feeding by using the remaining sheets.
In the third sheet feeding apparatus 20 of the related art, since the one sheet 21a is fed downstream in the sheet feeding direction A2 while being held between the auxiliary roller 26 and the lifting plate 23 as well as between the pair of transport rollers 27, there occurs a problem similar to that encountered in the first sheet feeding apparatus 1 of the related art. While the apparatus is constructed so that the sheets 21 stacked on the lifting plate 23 are fed downstream in the sheet feeding direction A2 by separating one sheet 21 at a time by the feed roller 26 and the lifting plate 23, simultaneous feeding of a plurality of sheets 21, that is, double feeding, may occur depending on the number of sheets 21. Furthermore, with the presence of the limiting plate 22a, the sheet 21 may be deflected along the limiting plate 22a, restraining the feeding of the sheet 21 toward the downstream side in the sheet feeding direction A2, and this can result in a misfeed condition in which the sheet 21 is not fed out.
In the fourth sheet feeding apparatus of the related art, since the limiting plate 34, a plate-like member, is fixedly provided on the downstream side of the lifting plate 32 as viewed in the sheet feeding direction A3, the feeding of the sheet 31 in the downstream direction along the sheet feeding direction A3 may be restrained, resulting in a misfeed condition in which the sheet 31 is not fed out. Furthermore, the apparatus is constructed so that the sheets 31 stacked on the lifting plate 32 are fed downstream in the sheet feeding direction A3 by separating one sheet 31 at a time by the feed roller 33 and the lifting plate 32 but, when the plurality of sheets 31 are fed downstream in the sheet feeding direction A3 by the feed roller 33, the sheets may not be able to be separated by the limiting plate 34, resulting in a double feed, a phenomenon in which more than one sheet 31 is fed out simultaneously.
In the fifth sheet feeding apparatus 40 of the related art, when transporting the one sheet 41a by the pair of transport rollers, the holding of the one sheet 41a by the feed roller 43 and the separator plate 46 is released, and the remaining sheets are not held between the feed roller 43 and the separator plate 46; this can also result in a double feed condition in which more than one remaining sheet is fed out simultaneously by the feed roller 43 in the downstream direction along the sheet feeding direction A4.
In the sixth sheet feeding apparatus 50 of the related art, since the one sheet 51a is transported downstream in the sheet feeding direction A while being held between the idle roller 54 and the lifting plate 52 as well as between the pair of transport rollers, back tension occurs, and this can cause a problem similar to that encountered in the first sheet feeding apparatus 1 of the related art.
In the sheet feeding apparatuses 1, 15, 20, 30, 40, and 50 of the related art, since trouble occurs when feeding sheets, or more specifically, when feeding one sheet, as described above, the sheet cannot be fed accurately and stably. Furthermore, in the related art, there is disclosed no apparatus that can simultaneously achieve the separation of the remaining sheets, excluding the one sheet, from the feed roller, the separation of the separator plate from the feed roller, and the restraining of the movement of the remaining sheets in the downstream direction along the sheet feeding direction, after the one sheet closest to the feed roller has been separated by the separator plate.